Inspectors, acting on data from the CIA, have yet to substantiate U.S. allegations. Still, their report to the U.N. will raise several concerns.

WASHINGTON — After two months and more than 350 inspections, United Nations weapons teams in Iraq have so far been unable to corroborate Bush administration claims that Saddam Hussein is secretly building chemical, biological or nuclear weapons.

In particular, inspectors have found no proof of prohibited activities at a series of suspect sites -- including nuclear facilities, chemical factories and missile production plants -- that the CIA publicly identified last fall.

The U.N. inspectors, however, have also been unable to resolve scores of crucial questions about Iraq's former weapons programs, including the location of 1.5 tons of VX nerve gas, 2 tons of anthrax growth media, 400 bombs for germ warfare agents and 550 artillery shells filled with mustard gas.

The teams have confirmed that over the last four years, Iraq illicitly obtained hundreds of missile engines without U.N. approval, as well as raw materials for rocket fuel and chemical agents. Such imports, as well as Iraq's failure to provide an accurate account of its weapons programs, are a violation of U.N. resolutions aimed at disarming the Hussein regime, according to U.N. and U.S. officials.

That mix of results is likely to dominate Monday when Hans Blix, the chief U.N. weapons inspector, and Mohamed ElBaradei, head of the International Atomic Energy Agency, or IAEA, brief the U.N. Security Council on the first 60 days of inspections of Iraqi factories, laboratories, military facilities, presidential palaces and other sites.

Both men are expected to seek more time for inspectors to search at least 350 more sites in Iraq as well as to follow up current investigations. But they will also sharply criticize Iraq for refusing to provide new information on its past weapons programs and for refusing to allow U-2 high-altitude surveillance flights. U.N. arms teams in Iraq from 1991 to 1998 relied heavily on the American-operated spy planes for aerial reconnaissance.

Bush administration and intelligence officials insist that the failure to find illegal weapons so far simply proves that Iraq has hidden its weapons programs and arsenals in secret underground bunkers or in mobile laboratories. They say Iraq has stashed sensitive documents and other evidence in homes and farms, or under mosques and hospitals.

Such materials "are being moved constantly and hidden," Paul D. Wolfowitz, deputy secretary of Defense, told the Council on Foreign Relations think tank in New York on Thursday. Spy satellites have photographed trucks leaving facilities while inspections were going on, other officials say.

Hussein has ordered that any scientist who cooperates in interviews "will be killed, as well as their families," Wolfowitz said. "Furthermore, we know that scientists are being tutored on what to say to the U.N. inspectors and that Iraqi intelligence officers are posing as scientists to be interviewed by the inspectors."

U.S. Shares Limited Data

The Bush administration, which has largely refused to release specific evidence to the public to support its claims, began sharing a limited amount of intelligence with the U.N. teams this month. Officials said they have provided specific information and tips about individuals and facilities that allegedly are part of Hussein's illegal weapons programs, and have suggested ways to investigate them.

But inspectors in Iraq from the U.N. and the IAEA, the U.N.'s nuclear watchdog, have found little that appears to support the widely publicized U.S. assertions. To be sure, some sites are still under investigation, some results may not yet be public, and Iraq may have hidden or moved material after media reports highlighted U.S. concerns. But several of the most prominent claims appear to have been disproved.

The CIA warned in an unclassified report in October, for example, that Iraq appeared to be "reconstituting" its clandestine nuclear weapons program. As evidence, officials cited commercial satellite photos that showed new construction at Al Tuwaitha, a former nuclear weapons complex that was heavily bombed during the 1991 Persian Gulf War. Such photos, President Bush said in Cincinnati on Oct. 7, "reveal that Iraq is rebuilding facilities at sites that have been part of its nuclear program in the past."

Experts from the IAEA have visited Al Tuwaitha 12 times since December, most recently Tuesday. They have checked equipment, sampled soil and water, conducted radiation surveys, shown up at night and on a Muslim holiday and carried out numerous other tests.

No improper activities have been found so far, according to preliminary U.N. reports. On Dec. 20, a joint U.N. and IAEA statement declared that the former Al Tuwaitha nuclear complex "now conducts civilian research in the nonnuclear field." A British journalist who visited the site, about 15 miles south of Baghdad, reported that the new buildings "appeared to be no more than a few sheds."